The present invention broadly relates to removable fluid filters and, more specifically pertains to a new and improved filtering apparatus or filter having a filtering material arranged in pleated or zig-zag form.
Generally speaking, the apparatus of the present invention is of the type comprising at least one filtering material pleated in fanfold or zig-zag manner and arranged between the inflow or upstream side and the outflow or downstream side of the filtering apparatus.
Such a filtering apparatus is known, for example, from German Published Patent Application No. 2,900,081, published July 19, 1979. A two-component filtering element pleated in zig-zag formation is arranged between the inlet side and the outlet side of the filter. The inner or downstream component of the two-component filtering element is a flexible thin supporting layer of high mechanical strength. The pleated filtering layer and the pleated supporting layer are in surface-to-surface contact at least during filtration of a medium passing from the filtering layer to the supporting layer, without these layers being connected or joined to one another. During a cleaning operation, a flow of cleansing medium, which is often compressed air, is directed in the opposite direction from the inner supporting layer to the outer filtering layer. The filtering layer is thereby inflated such that the filtering pleats which are open toward the operational inflow side narrow or converge and the separation of the filter cake consisting of the filtered-out material is rendered difficult if not impossible due to the material wedged or lodged between the contiguous sides of the filtering pleats. In those instances where there occurs a failure to remove such enclosed portions of the filter cake, then, the pressure of the cleansing medium is increased, but this can cause the filtering material to tear or rupture. This known filter possesses a relatively complicated and expensive two-component combination of a filtering layer and a supporting layer and can be therefore generally considered uneconomical to manufacture.
A further filter element or filter is known from Swiss Pat. No. 619,152, published Sept. 15, 1980. The filter disclosed therein consists of an inner layer of filtering paper and an outer supporting layer arranged at the inflow or upstream side of the filtering paper. Both layers are adhesively bonded to one another. This relatively expensive design is also uneconomical to manufacture. In a cleaning operation for this filter, there is normally provided compressed air which flows in a direction opposite to the direction of flow of the medium to be filtered, in order that the filter cake is separated from the filter surface. In this known filter, the filter cake is located at the surface of the pleated stiff supporting layer and a relatively high pressure of the cleansing medium must be provided to remove such filter cake. This would require correspondingly costly pressure generating and distributing devices as well as a corresponding constructional expenditure for the provision of the requisite safety measures or arrangements. The filter cake is difficult to remove from the stiff supporting layer formed of expanded material, in the mesh of which the filter cake is lodged or anchored.
An insert for fluid filter cartridges having a pleated filtering material arranged at the inflow or upstream side of a solid supporting body pervious to gas and/or liquids is known, for example, from U.S. Pat. No. 3,302,796, granted Feb. 7, 1967. At the outflow or downstream side of the filtering material, wherein such outflow or downstream side faces the supporting body, there is provided in each filtering pleat or fold, a dimensionally stable insert or spacer formed of a flat sheet of material provided with bilaterally or double-sided protuberant deformations. Such a flat sheet of material can be formed of metal or plastic material and the inserts or spacers can possess, for example, a corrugated or zig-zag configuration. The wave troughs or zig-zag edges extend perpendicular or inclined to the surface of the supporting body. On the other hand, such inserts or spacers formed of a flat sheet of material are provided with bilaterally or double-sided projecting dimple-shaped protuberances. Upon throughflow and filtration of a highly viscous liquid by means of the still clean filtering material, or upon throughflow of a low viscous liquid or of a gas through the soiled and clogged filtering material, the filtering material is pressed against the surface of the inserts or spacers and the filtering material adapts to the protuberant surfaces of such inserts or spacers. Since the filtering material does not permit any throughflow at the locations pressed against the inserts or spacers, because the underlying inserts or spacers are impervious to liquids and/or gases, the flow resistance of the entire fluid filter cartridge increases such that the pressure at the inflow or upstream side of the filtering material increases even further. As a result, the filtering material is pressed to an even greater extent against the impervious inserts or spacers, thus decreasing the filtering effect of the fluid filter cartridge.